Error messge: Generation has thrown an exception: list index out of range when wanting to generate rig
My best guess: you tried to partially delete the face.
Unfortunately you can't selectively delete parts of the face (as of 2.82a, later versions may provide more flexibility). 
Either keep the whole face or delete all bones that belong to it.  

Some info may be found here:
https://developer.blender.org/T53842